1,003 research outputs found
First direct mass-measurement of the two-neutron halo nucleus 6He and improved mass for the four-neutron halo 8He
The first direct mass-measurement of He has been performed with the
TITAN Penning trap mass spectrometer at the ISAC facility. In addition, the
mass of He was determined with improved precision over our previous
measurement. The obtained masses are (He) = 6.018 885 883(57) u and
(He) = 8.033 934 44(11) u. The He value shows a deviation from
the literature of 4. With these new mass values and the previously
measured atomic isotope shifts we obtain charge radii of 2.060(8) fm and
1.959(16) fm for He and He respectively. We present a detailed
comparison to nuclear theory for He, including new hyperspherical harmonics
results. A correlation plot of the point-proton radius with the two-neutron
separation energy demonstrates clearly the importance of three-nucleon forces.Comment: 4 pages, 2 figure
First Penning-trap mass measurement in the millisecond half-life range: the exotic halo nucleus 11Li
In this letter, we report a new mass for Li using the trapping
experiment TITAN at TRIUMF's ISAC facility. This is by far the shortest-lived
nuclide, , for which a mass measurement has ever been
performed with a Penning trap. Combined with our mass measurements of
Li we derive a new two-neutron separation energy of 369.15(65) keV: a
factor of seven more precise than the best previous value. This new value is a
critical ingredient for the determination of the halo charge radius from
isotope-shift measurements. We also report results from state-of-the-art
atomic-physics calculations using the new mass and extract a new charge radius
for Li. This result is a remarkable confluence of nuclear and atomic
physics.Comment: Formatted for submission to PR
Collisional perturbation of radio-frequency E1 transitions in an atomic beam of dysprosium
We have studied collisional perturbations of radio-frequency (rf)
electric-dipole (E1) transitions between the nearly degenerate opposite-parity
levels in atomic dysprosium (Dy) in the presence of 10 to 80 Torr of
H, N, He, Ar, Ne, Kr, and Xe. Collisional broadening and
shift of the resonance, as well as the attenuation of the signal amplitude are
observed to be proportional to the foreign-gas density with the exception of
H and Ne, for which no shifts were observed. Corresponding rates and cross
sections are presented. In addition, rates and cross sections for O are
extracted from measurements using air as foreign gas. The primary motivation
for this study is the need for accurate determination of the shift rates, which
are needed in a laboratory search for the temporal variation of the
fine-structure constant [A. T. Nguyen, D. Budker, S. K. Lamoreaux, and J. R.
Torgerson, Phys. Rev. A \textbf{69}, 22105 (2004)].Comment: 11 pages, 8 figure
Phase diagram of heavy fermion systems
The Meccano of heavy fermion systems is shown on different cases going from
anomalous monochalcogenides to cerium intermetallic compounds with special
focus on the ideal case of the CeRu2Si2 series. Discussion is made in the frame
of the interplay between valence, electronic structure (Fermi surface), and
magnetism. The nice tools given by the temperature, the pressure, and the
magnetic field allow to explore different ground states as well as the slow
downhill ''race'' before reaching a Fermi liquid finish line at very low
temperature. Experimentally, the Gr"uneisen parameter i.e. the ratio of the
thermal expansion by the specific heat is a coloured magic number; its
temperature, pressure, and magnetic field dependence is a deep disclosure of
competing hierarchies and the conversion of this adaptive matter to external
responses.Comment: submitted ICM200
Discontinuous Transition from a Real Bound State to Virtual Bound State in a Mixed-Valence State of SmS
Golden SmS is a paramagnetic, mixed-valence system with a pseudogap. With
increasing pressure across a critical pressure Pc, the system undergoes a
discontinuous transition into a metallic, anti-ferromagnetically ordered state.
By using a combination of thermodynamic, transport, and magnetic measurements,
we show that the pseudogap results from the formation of a local bound state
with spin singlet. We further argue that the transition Pc is regarded as a
transition from an insulating electron-hole gas to a Kondo metal, i.e., from a
spatially bound state to a Kondo virtually bound state between 4f and
conduction electrons.Comment: 5 pages, 5 figure
Nitric oxide co-operates with hydrogen peroxide in inducing DNA fragmentation and cell lysis in murine lymphoma cells
Two chemically distinct root lignin barriers control solute and water balance.
Lignin is a complex polymer deposited in the cell wall of specialised plant cells, where it provides essential cellular functions. Plants coordinate timing, location, abundance and composition of lignin deposition in response to endogenous and exogenous cues. In roots, a fine band of lignin, the Casparian strip encircles endodermal cells. This forms an extracellular barrier to solutes and water and plays a critical role in maintaining nutrient homeostasis. A signalling pathway senses the integrity of this diffusion barrier and can induce over-lignification to compensate for barrier defects. Here, we report that activation of this endodermal sensing mechanism triggers a transcriptional reprogramming strongly inducing the phenylpropanoid pathway and immune signaling. This leads to deposition of compensatory lignin that is chemically distinct from Casparian strip lignin. We also report that a complete loss of endodermal lignification drastically impacts mineral nutrients homeostasis and plant growth
Intra-Host Evolution Analyses in an Immunosuppressed Patient Supports SARS-CoV-2 Viral Reservoir Hypothesis.
Throughout the SARS-CoV-2 pandemic, several variants of concern (VOCs) have been identified, many of which share recurrent mutations in the spike glycoprotein's receptor-binding domain (RBD). This region coincides with known epitopes and can therefore have an impact on immune escape. Protracted infections in immunosuppressed patients have been hypothesized to lead to an enrichment of such mutations and therefore drive evolution towards VOCs. Here, we present the case of an immunosuppressed patient that developed distinct populations with immune escape mutations throughout the course of their infection. Notably, by investigating the co-occurrence of substitutions on individual sequencing reads in the RBD, we found quasispecies harboring mutations that confer resistance to known monoclonal antibodies (mAbs) such as S:E484K and S:E484A. These mutations were acquired without the patient being treated with mAbs nor convalescent sera and without them developing a detectable immune response to the virus. We also provide additional evidence for a viral reservoir based on intra-host phylogenetics, which led to a viral substrain that evolved elsewhere in the patient's body, colonizing their upper respiratory tract (URT). The presence of SARS-CoV-2 viral reservoirs can shed light on protracted infections interspersed with periods where the virus is undetectable, and potential explanations for long-COVID cases
Reassessment of the Lineage Fusion Hypothesis for the Origin of Double Membrane Bacteria
In 2009, James Lake introduced a new hypothesis in which reticulate phylogeny reconstruction is used to elucidate the origin of Gram-negative bacteria (Nature 460: 967–971). The presented data supported the Gram-negative bacteria originating from an ancient endosymbiosis between the Actinobacteria and Clostridia. His conclusion was based on a presence-absence analysis of protein families that divided all prokaryotes into five groups: Actinobacteria, Double Membrane bacteria (DM), Clostridia, Archaea and Bacilli. Of these five groups, the DM are by far the largest and most diverse group compared to the other groupings. While the fusion hypothesis for the origin of double membrane bacteria is enticing, we show that the signal supporting an ancient symbiosis is lost when the DM group is broken down into smaller subgroups. We conclude that the signal detected in James Lake's analysis in part results from a systematic artifact due to group size and diversity combined with low levels of horizontal gene transfer.Exobiology Program (U.S.) (Grant NNX08AQ10G)Assembling the Tree of Life (Program) (Grant DEB 0830024
- …